This invention, which is based on research supported by the U.S. Public Health Service, National Institutes of Health, relates to the field of gels and, in particular, to gels prepared from emulsions containing an oleophilic, hydrophobic dispersed phase and an aqueous continuous phase. These gels, when treated with aqueous media, spontaneously regenerate oil-in-water emulsions similar to the ones from which they were prepared. The invention also relates to processes for preparing gel compositions from emulsions and reconstituting emulsions from the gels by addition of water to the latter.
Emulsions, because of their instability, have relatively limited application as dosage forms. This is so despite the fact that the bioavailability of slightly soluble oral drugs, which are often absorbed incompletely in the gastro-intestinal tract because of their low solubility, is known to be considerably enhanced by dissolving such drugs in vegetable oils and emulsifying these oily solutions in water. Drug absorption from such emulsions is much faster and more complete than when these drugs are incorporated into tablets or capsules.
The reason that emulsions are not used more widely as vehicles for oral drugs is that their shelf-life is relatively brief, i.e., the oil droplets cream and coalesce on standing.
U.S. Pat. No. 4,066,568 describes the manufacture of microcapsules by dispersing and emulsifying hydrophobic materials containing medicines or color-forming materials which are insoluble in water, with the aid of gelatin and a coarcervating agent to make a coating film around the hydrophobic core. The production of gels which are stable on storage is described in U.S. Pat. No. 4,160,754, although by a different method comprising the use of a polymer matrix, a liquid dispersing agent and optional fibers. This patent discloses the use of gels for various purposes including perfume carriers, paddings and shock-absorbers.
Both Rehfeld, Journal of Colloid and Interface Science, 46, No. 3, 448-458 (March 1974) and Vold, et al., ibid., 65, No. 2, 390-393 (June 15, 1978) describe the ultracentrifugation of oil-in-water emulsions but are silent with respect to the presence of a gel fraction. Garrett, J. Soc. Cosmet. Chem., 21, 393-415 (May 27, 1970) describes the use of ultracentrifugation in evaluating the stability and properties of oil-in-water emulsions. While brief mention is made of the appearance, following ultracentrifugation, of a "translucent cream" along with an opaque cream layer, there is no indication in this publication of the presence of a gel layer, possibly due to the fact that the boundary between any gel which may have formed and coalesced oil is very faint and only evident to the touch and upon standing, such gel as may have formed may have reverted to cream layers thereby escaping observation.